Lighting system, particularly for use in extreme ultraviolet (EUV) lithography

ABSTRACT

A lighting system, particularly for use in extreme ultraviolet (EUV) lithography, comprising a projection lens for producing semiconductor elements for wavelengths ≦193 nm is provided with a light source, an object plane, an exit pupil, a first optical element having first screen elements for producing light channels, and with a second optical element having second screen elements. A screen element of the second optical element is assigned to each light channel that is formed by one of the first screen elements of the first optical element. The screen elements of the first optical element and of the second optical element can be configured or arranged so that they produce, for each light channel, a continuous beam course from the light source up to the object plane. The angles of the first screen elements of the first optical element can be adjusted in order to modify a tilt. The location and/or angles of the second screen elements of the second optical element can be adjusted individually and independently of one another in order to realize another assignment of the first screen elements of the first optical element to the second screen elements of the second optical element by displacing and/or tilting the first and second screen elements.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. §371 of and claims priority to PCTInternational Application Number PCT/EP 03/003616, which was filed 08Apr. 2003 (08.04.03), and was published in German which was based onGerman Patent Application No. 102 19 514.5 which was filed 30 Apr. 2002(30.04.02) and the teachings of which are incorporated herein byreference.

The invention relates to a lighting system, in particular for extremeultraviolet (EUV) lithography, comprising a projection objective forproducing semiconductor elements for wavelengths ≦193 mm, a lightsource, an object plane, an exit pupil, the first optical element havingfirst grid elements for producing optical channels and the secondoptical element having second grid elements, each optical channel whichis formed by one of the first grid elements of the first optical elementbeing assigned a grid element of the second optical element, it beingpossible for grid elements of the first optical element and of thesecond optical element to be configured in such a way or arranged insuch a way that the result for each optical channel is a continuous beamcourse from the light source as far as the object plane.

The invention also relates to a projection exposure installation havingsuch a lighting system.

In order to reduce the structure widths of electronic components, inparticular of semiconductor components, the wavelength for the lightused for the microlithography should be reduced further and further. Atpresent, wavelengths of ≦193 nm are already used in lithography.

Here, a lighting system suitable for EUV Lithography should illuminatethe field predefined for the EUV lithography, in particular the annularfield of an objective, homogeneously, that is to say uniformly, with asfew reflections as possible. In addition, the pupil of the objectiveshould be illuminated independently of the field as far as a specificfilling level σ, and the exit pupil of the lighting system should lie inthe entry pupil of the objective.

With regard to the general prior art, reference is made to U.S. Pat.Nos. 5,339,346, 5,737,137, 5,361,292 and 5,581,605.

EP 0 939 341 shows a lighting system for the EUV range having a firstoptical integrator, which has a large number of first grid elements, anda second optical integrator, which has a large number of second gridelements. In this case, the distribution of the illumination in the exitfield is controlled via a stop wheel. However, the use of a stop wheelentails considerable light losses. Further solutions proposed, such as aquadrupole illumination distribution and illumination systems that canbe used differently via interchangeable optics are, however, firstlyvery complex and secondly restricted to specific types of illumination.

DE 199 03 807 A1 describes an EUV lighting system which, inter alia,comprises two mirrors having grid elements. Systems of this type arealso designated double-facetted EUV lighting systems. The illuminationof the exit pupil is in this case determined by the arrangement of thegrid elements on the second mirror. The illumination in the exit pupilor an illumination distribution is in this case defined.

In the earlier German patent application 100 53 587.9 a lighting systemis described, it being possible for a predefined illumination pattern tobe set in the exit pupil of the lighting system by means of appropriateassociations between the grid elements of the first and of the secondoptical element. Using a lighting system of this type, the field in thereticle plane can be illuminated homogeneously and with a partiallyfilled aperture, and also the exit pupil of the lighting system can beilluminated in a variable manner. The variable setting of any desiredillumination distribution in the exit pupil is in this case carried outlargely without light losses.

The present invention is based on the object of providing a lightingsystem with which the basic idea of the earlier patent application canbe implemented in practice by means of constructional solutions.

According to the invention, this object is achieved in that the anglesof the first grid elements of the first optical element can be adjustedin order to modify a tilt. In addition, the location and/or angle of thesecond grid elements of the second optical element can also be adjustedindividually and independently of one another, in order, by means ofdisplacing and/or tilting the first and second grid elements, toimplement a different assignment of the first grid elements of the firstoptical element to the second grid elements of the second opticalelement.

By means of appropriate displacement and/or tilting of the gridelements, optical channels in variable configurations can now beachieved.

In order that the individual bundles of rays of field honeycombs as gridelements in the field overlap again, pupil honeycombs as grid elementscan be inclined or tilted appropriately in relation to a pupil honeycombplate or the mirror support of the latter. Mirror facets areparticularly suitable as field honeycombs and as pupil honeycombs.

If, in this case, the system is built up as a system having realintermediate images of the light source after the field honeycomb plateor the mirror support of the first optical element, then the pupilhoneycombs can be used at the same time as field lenses for the coupledprojection of the light source into the entry pupil of the lithographyobjective or projection objective.

If, in an advantageous refinement of the invention, the number M ofsecond grid elements (pupil honeycombs) of the pupil honeycomb plate orthe mirror support is always greater than N, where N is the number ofchannels, which is determined by the number of illuminated first gridelements (field honeycombs), variable illumination patterns can bepresented in the exit pupil. In other words: in this case, more pupilhoneycombs or mirror facets will be provided on the second opticalelement than would be necessary for the number of optical channelsproduced by the first grid elements of the first optical element. Givena specific setting with a specific field honeycomb having N channels, ineach case only some of the pupil honeycombs are thus illuminated. Thistherefore leads to segmented or parceled illumination of the pupilhoneycombs.

Further advantageous refinements and developments of the inventionemerge from the remaining subclaims and from the following exemplaryembodiments described in principle by using the drawing, in which:

FIG. 1 shows a structure of an EUV lighting system having a lightsource, a lighting system and a projection objective;

FIG. 2 shows a basic sketch of the beam path having two mirrors withgrid elements in the form of mirror facets and a collector unit;

FIG. 3 shows a basic sketch of another beam path having two mirrors withgrid elements in the form of mirror facets and a collector unit;

FIG. 4 shows a plan view of the first optical element in the form of afield honeycomb plate (mirror support) having a large number of mirrorfacets;

FIG. 5 shows a plan view of the second optical element in the form of apupil honeycomb plate as mirror support having a large number of mirrorfacets with circular illumination;

FIG. 6 shows a plan view of the second optical element in the form of apupil honeycomb of plate having a large number of mirror facets withannular illumination;

FIG. 7 shows a plan view of a pupil honeycomb plate;

FIG. 8 shows a section along the line VIII—VIII from FIG. 7;

FIG. 9 shows a plan view of a pupil honeycomb plate which is constructedas a control disk;

FIG. 10 shows a section along the line X—X from FIG. 9;

FIG. 11 shows an enlarged illustration in section of a mirror facethaving a solid body joint;

FIG. 12 shows a plan view of the mirror facet according to FIG. 11;

FIG. 13 shows an enlarged illustration in section of a mirror facethaving another type of mounting; and

FIG. 14 shows a plan view of the mirror facet according to FIG. 13.

FIG. 1 shows in a general illustration an EUV projection lightinginstallation having a complete EUV lighting system comprising a lightsource 1, for example a laser-plasma, plasma or pinch-plasma source orelse another EUV light source, and a projection objective 25 illustratedmerely in principle. Apart from the light source 1, there are arrangedin the lighting system a collector mirror 2 which, for example, cancomprise a plurality of shells arranged in one another, a planar mirror3 or reflective spectral filter, an aperture stop 4 with an image of thelight source (not designated), a first optical element 5 having a largenumber of facet mirrors 6 (see FIGS. 2 and 3), a second optical element7 arranged thereafter and having a large number of grid elements 8 inthe form of facet mirrors, and two projection mirrors 9 a and 9 b. Theprojection mirrors 9 a and 9 b are used to project the facet mirrors 8of the second optical element 7 into an entry pupil of the projectionobjective 25. The reticle 12 can be moved in the y direction as ascanning system. The reticle plane 11 also simultaneously constitutesthe object plane.

In order to provide different optical channels for adjusting the settingin the bean path of the lighting system, for example there is a largernumber M of mirror facets 8 of the second optical element 7 thancorresponds to the number N of the mirror facets 6 of the first opticalelement 5. In FIG. 1, the mirror facets are not illustrated, for reasonsof clarity. The angles of the mirror facets 6 of the first opticalelement 5 can in each case be adjusted individually, while both theangles and the locations of the mirror facets 8 of the second opticalelement 7 can be adjusted. In FIGS. 7 to 14, explained in the followingtext, details relating to this are described and illustrated. As aresult of the tiltable arrangement and the ability to displace themirror facets 6 and 8, different beam paths and thus different opticalchannels can be created between the first optical element 5 and thesecond optical element 7.

The following projection objective 25 can be constructed as a six-mirrorprojection objective. A wafer 14 is located on a carrier unit 13 as theobject to be exposed.

As a result of the ability to adjust the mirror facets 6 and 8,different settings can be implemented in an exit pupil 15 of thelighting system which, at the same time, forms an entry pupil of theprojection objective 25.

In FIGS. 2 and 3, optical channels which are different in principle areillustrated by means of different layers and angles of the mirror facets6 and 8 of the two optical elements 5 and 7. The lighting system is inthis case indicated in simplified form as compared with the illustrationin FIG. 1 (for example with respect to the position of the opticalelements 5 and 7 and with only one projection mirror 9).

In this case, the illustration in FIG. 2 shows a greater filling factorσ.

-   -   For σ=1.0, the objective pupil is filled completely;    -   σ=0.6 accordingly denotes underfilling.

In FIGS. 2 and 3, the beam path from the light source 1 via the reticle12 as far as the exit pupil 15 is illustrated.

FIG. 4 shows a plan view of a mirror support 16 of the first opticalelement 5 having a large number of grid elements in the form of mirrorfacets 6. The illustration shows 142 individually adjustable mirrorfacets 6 as field honeycombs in rectangular form, which are arranged inblocks in a region illuminated by the nested collector mirror 2. Theangles of the mirror facets 6 can in each case be adjusted individually.The facets 8 of the second optical element 7 can additionally bedisplaced among themselves and, if required, also independently of oneanother.

FIG. 5 shows a plan view of a mirror support 16 or pupil honeycomb plateof the second optical element 7, the optical channels resulting in acircular setting.

FIG. 6 shows a plan view of a mirror support 16 of the second opticalelement 7 having mirror facets in an annular setting. A furtherpossibility consists in a known quadrupole setting (not illustrated). InFIGS. 5 and 6, the illuminated mirror facets are in each caseillustrated dark.

FIG. 7 shows a plan view of the mirror support 16 of the second opticalelement 7, the mirror support 16 being formed as a guide disk. Themirror support 16 or the guide disk is provided with a large number ofguide grooves (only one guide groove 17 is illustrated in FIG. 7, forreasons of clarity), in which a circular mirror facet 8 is guided ineach case. The guide groove 17 runs essentially radially or in slightlycurved form for this purpose. The course of the guide grooves 17 dependson the respective application and on the desired displacement directionof the mirror facets 8.

Underneath the mirror support 16 or the guide disk, parallel to andresting thereon, there is arranged a control disk 18, which is likewiseprovided with a number of control grooves 19 corresponding to the guidegrooves 17 and therefore to the mirror facets 8. Each mirror facet 8 isthus guided in a guide groove 17 and in a control groove 19. If thecontrol disk 18 is moved in the direction of the arrow 20 in FIG. 7 bymeans of a drive device, not illustrated, then the mirror facets 8 aremoved radially inward or outward along the guide groove 17. As a resultof this displacement, the assignments of the optical channels andtherefore the illumination change. This means that, by rotating thecontrol disk 18 relative to the guide disk 16, the associated mirrorfacet 8 at the point of intersection of the two grooves 17 and 19 isdisplaced along the associated guide groove 17.

FIGS. 9 and 10 show a refinement for the displacement of the mirrorfacets 8 of the second optical element 7 respectively in a guide groove17 of the mirror support 16, in each case a drive device 21 beingprovided (illustrated only in principle and dashed in FIGS. 9 and 10).In this case, each mirror facet 8 has its own drive in the associatedguide groove 17, it being possible for the drive to be provided, forexample, in accordance with the known piezoelectric inch-worm principle.

Of course, for this purpose, other drive devices by means of which themirror facets 8 can be adjusted individually in each case are alsopossible. Instead of arranging the drive device in each case directly ina guide groove 17, if required these can of course also be arrangedindependently thereof underneath or behind the mirror support 16.

FIGS. 11 and 12 illustrate in section and in plan view an enlargedillustration of a mirror facet 6 of the first optical element 5, whichis connected to the mirror support 16 of the first optical element 5 bya joint 22, which is formed as a solid body joint. In this case, all theparts can be in one piece or each mirror facet 6 has a central web as ajoint 22, via which the connection is made to the mirror support 16located underneath.

By means of actuators 23, not specifically illustrated, which arelocated between the mirror support 16 and the underside of each mirrorfacet 6, each mirror facet 6 can be tilted with respect to the mirrorsupport 16. The plan view according to FIG. 12 reveals that tiltingpossibilities in both directions are provided by an actuator 23 which islocated on the y axis and a further actuator 23 which is located on thex axis. In this case, the two actuators 23 are in each case located onthe axis assigned to them outside the point of intersection of the axes.

Since the adjustment or tilting of each mirror facet 6 is carried outonly to a very small extent, piezoceramic elements, for example, can beused as actuators 23.

FIGS. 13 and 14 illustrate a refinement by means of which larger tiltsfor the mirror facets 6 are made possible. As can be seen from FIG. 13,in this case there is a central tilting joint or tilting bearing 24between the mirror facet 6 and the mirror support 16. Here, too,actuators 23 ensure that the mirror facets 6 are tilted both in the xdirection and in the y direction. For this purpose, in this case thereare two actuators 23 arranged at a distance from each other on the yaxis outside the point of intersection of the two axes, and two furtheractuators 23 outside the y axis on both sides at the same distance fromthe x axis (see FIG. 14).

By means of the tilting devices illustrated in FIGS. 11 to 14, t ispossible to adjust not only the mirror facets 6 of the first opticalelement 5 but also the mirror facets 8 of the second optical element 7as desired and independently of one another.

As distinct from the mirror facets 6 of the first optical element 5,which have an elongated or narrow rectangular form, the mirror facets 8of the second optical element 7 have a circular form. However, thisdifference has no influence on the type or mode of action of the tiltingdevices illustrated in FIGS. 11 to 14.

In principle, the mirror facets 6 of the first optical element canlikewise be displaced in the same way as illustrated in FIGS. 7 to 10but, in practice, this will generally not be necessary; instead, puretilting adjustments will as a rule be sufficient.

Actuating elements that can be activated magnetically or electricallyare also possible as actuators 23. The actuators 23 can in this caseadjust the mirror facets 6 and 8 continuously via a control loop (notillustrated). Likewise, it is also possible for the actuators to defineend positions, with which in each case two exact tilted positions arepredefined for the mirror facets 6 and 8.

1. A lighting system, in particular for EUV lithography, comprising aprojection objective for producing semiconductor elements forwavelengths ≦193 nm, a light source, an object plane, an exit pupil, afirst optical element having first grid elements for producing opticalchannels and a second optical element having second grid elements, eachoptical channel which is formed by one of the first grid elements of thefirst optical element being assigned a grid element of the secondoptical element, it being possible for grid elements of the firstoptical element and of the second optical element to be configured insuch a way or arranged in such a way that the result for each opticalchannel is a continuous beam course from the light source as far as theobject plane, characterized in that the angles of the first gridelements of the first optical element can be adjusted in order to modifya tilt in order, by means of tilting the first grid elements, toimplement a different assignment of the first grid elements of the firstoptical element to the second grid elements of the second opticalelement.
 2. The lighting system as claimed in claim 1, characterized inthat the number M of second grid elements of the second optical elementis greater than the number N of first grid elements of the first opticalelement.
 3. The lighting system as claimed in claim 1 or 2,characterized in that the location and/or the angle of the second gridelements of the second optical element can be adjusted individually andindependently of one another in order, by means of displacement and/ortilting of the first and second grid elements, to implement a differentassignment of the first grid elements of the first optical element tothe second grid elements of the second optical element.
 4. The lightingsystem as claimed in claim 3, characterized in that the first gridelements are formed as field honeycombs in the form of first mirrorfacets, and in that the second grid elements are formed as pupilhoneycombs in the form of second mirror facets, the first mirror facetsand the second mirror facets in each case being arranged on a mirrorsupport.
 5. The lighting system as claimed in claim 4, characterized inthat the optical channels between the mirror facets of the first and thesecond optical element can be adjusted by tilting the first mirrorfacets of the first optical element in relation to the mirror support,in order in this way to implement different assignments of the firstmirror facets of the first optical element to the second mirror facetsof the second optical element and therefore different illuminationpatterns of an exit pupil.
 6. The lighting system as claimed in claim 4or 5, characterized in that the optical channels between the firstmirror facets of the first optical element and the second mirror facetsof the second optical element can be adjusted by tilting and displacingthe second mirror facets of the second optical element in relation tothe mirror support.
 7. The lighting system as claimed in claim 4,characterized in that the mirror facets of the first optical elementand/or of the second optical element are in each case connected to theassociated mirror support via a joint.
 8. The lighting system as claimedin claim 7, characterized in that the joints are formed as solid bodyjoints.
 9. The lighting system as claimed in claim 7 or 8, characterizedin that the mirror facets can be tilted in the x direction and/or in they direction.
 10. The lighting system as claimed in claim 9,characterized in that the joints are in each case located on the x axisand/or the y axis of the mirror facets.
 11. The lighting system asclaimed in claim 4, characterized in that, in order to displace and/ortilt the mirror facets, actuators are arranged between the grid elementsand the mirror support.
 12. The lighting system as claimed in claim 11,characterized in that the actuators have piezoceramic adjustingelements.
 13. The lighting system as claimed in claim 12, characterizedin that the actuators are provided with actuating elements that can beactivated magnetically or electrically.
 14. The lighting system asclaimed in claim 11, characterized in that the actuators adjust the gridelements continuously via a control loop.
 15. The lighting system asclaimed in claim 11, characterized in that end positions are defined forthe actuators.
 16. The lighting system as claimed in claim 4,characterized in that the mirror facets can be displaced on predefinedpaths.
 17. The lighting system as claimed in claim 16, characterized inthat cam tracks, in which the mirror facets are guided individually ineach case, are introduced into the mirror support.
 18. The lightingsystem as claimed in claim 17, characterized in that the mirror supportis formed as a guide disk, which interacts with a control disk, in whichthere are arranged guide tracks for the displacement of the mirrorfacets.
 19. The lighting system as claimed in claimed 18, characterizedin that the control disk is driven.
 20. The lighting system as claimedin claimed 17, characterized in that each mirror facet is guided in acam track in the mirror support, and in that each mirror facet can bedriven individually by a drive element.
 21. The lighting system asclaimed in claim 20, characterized in that the drive element is in eachcase arranged in a cam track and each mirror facet is moved individuallyin accordance with the inch-worm principle.
 22. A projection exposureinstallation for microlithography for producing semiconductor elements,comprising a lighting system and comprising a projection objective forproducing semiconductor elements for wavelengths ≦193 nm, a lightsource, an object plane, an exit pupil, a first optical element havingfirst grid elements for producing optical channels and a second opticalelement having second grid elements, each optical channel which isformed by one of the first grid elements of the first optical elementbeing assigned a grid element of the second optical element, it beingpossible for grid elements of the first optical element and of thesecond optical element to be configured in such a way or arranged insuch a way that the result for each optical channel is a continuous beamcourse from the light source as far as the object plane, characterizedin that the angles of the first grid elements of the first opticalelement can be adjusted in order to modify a tilt in order, by means oftilting the first grid elements, to implement a different assignment ofthe first grid elements of the first optical element to the second gridelements of the second optical element.
 23. The projection exposureinstallation as claimed in claim 22, characterized in that the number Mof second grid elements of the second optical element is greater thanthe number N of first grid elements of the first optical element. 24.The projection exposure installation as claimed in claim 22 or 23,characterized in that the location and/or the angle of the second gridelements of the second optical element can be adjusted individually andindependently of one another in order, by means of displacement and/ortilting of the first and second grid elements, to implement a differentassignment of the first grid elements of the first optical element tothe second grid elements of the second optical element.
 25. Theprojection exposure installation as claimed in claim 24, characterizedin that the first grid elements are formed as field honeycombs in theform of first mirror facets, and in that the second grid elements areformed as pupil honeycombs in the form of second mirror facets, thefirst mirror facets and the second mirror facets in each case beingarranged on a mirror support.
 26. The projection exposure installationas claimed in claim 25, characterized in that the optical channelsbetween the mirror facets of the first and the second optical elementcan be adjusted by tilting the mirror facets of the first opticalelement in relation to the mirror support, in order in this way toimplement different assignments of the first mirror facets of the firstoptical element to the second mirror facets of the second opticalelement and therefore different illumination patterns of an exit pupil.27. The projection exposure installation as claimed in claim 25 or 26,characterized in that the optical channels between the first mirrorfacets of the first optical element and the second mirror facets of thesecond optical element can be adjusted by tilting and displacing thesecond mirror facets of the second optical element in relation to themirror support.